Electrical recording medium



Feb. 25, 1964 e. MANDEL 3,122,433

ELECTRICAL RECORDING MEDIUM Filed Aug. 22, 1960 CURVE 4 SUM OF ORDINATES OF CURVES la 2 CURVE a (MAGANOUS CHLORIDE AND GALLIG ACID) P (Ta CURVE 2 z (GALLIC ACID) Lu 0 1 g g CURVE (MANGANOUS CHLORIDE) CURRENT Gem Id. Mmw l INVENTOR BY D 1 d3 Ni Cr Ag Su Pb Tl V It should be noted that these metals have a stable lower oxidation state in solution and are capable of being oxidized to a higher intermediate oxidation state in the presence of base produced by electrolysis of water.

The organic compounds which may be used include polyhydroxyphenolic and aromatic polyamine compounds. The polyhydroxyphenolic compounds include gallic acid, catechol, gentisic acid, hy'droquinone, and pyrogallol. The aromatic polyamine compounds include o-phenylenediamine, p-phenylenedimaine, benzidine and salts thereof, tolidine hydrochloride, and diphenylarnine hydrochloride.

Preferred formulations to impregnate about 30 square feet of white porous paper are set out hereinafter. The formulations when impregnated into about 30 square feet of White porous paper will be electrolytically markable upon passage of an electric current therethrough from electrodes applied to the paper. The electrodes need not be consumed in the marking process, and no supplementary heat is required to intensify the mark. The paper will dry out in air after marking, or drying may be accelerated by subjecting it to an air stream or a low-temperature heater bar.

Example #1 MI1C12-4 H2O g 4 NaCl g 10 C H O .H O (gallic acid) g 2 O cc 100 5 N NaOH cc 1 In the above formulation the manganous chloride can be replaced by manganous sulfate, manganous nitrate or other manganous salts.

Example #2 H2O g 4 NaCl g C7H605-H2O (gallic acid) g 2 5 N NaOH cc 1 H O cc 100 In the above formulation the nickelous chloride can be replaced by nickelous sulfates, nickelous nitrates, or by other nickelous salts.

Example #3 COCI2-6 H2O g 4 NaCl g 10 C H O .H O (gallic acid) g 2 5 N NaOH cc 1 H O cc 100 In the above formulation the cobaltous chloride can be replaced by cobaltous sulfates, cobaltous nitrates, or by other cobaltous salts.

In any of the above formulations, instead of gallic acid, there may be substituted catechol, pyrogallol, or other suitable polyhydroxyphenolic compounds, such as, but not limited to, hydroquinone and gentisic acid, or suitable aromatic amines such as benzidine hydrochloride, tolidine hydrochloride, diphenylamine hydrochloride, o-phenylenediamine, and p-phenylenediamine.

Sodium chloride is used to provide an electrolyte. Other electrolytes may' be used alternatively, such as sodium and potassium nitrates and equivalent electrolytes well known in the art.

i In the above examples, the quantities given for sodium chloride may vary from zero to grams (the solubility limit) depending upon the degree of electrical conductivity desired. Similarly, if sodium nitrate is used for an electrolyte, its concentration may vary from zero to grams (the solubility limit).

The quantities given for the gallic acid represent the approximate solubility limit for this material. If less than this amount is used the intensity of the resulting mark is decreased.

The quantities of the nickelous, cobaltous and manganous salts or combinations thereof used may be varied up to their respective solubility limits.

Enough sodium hydroxide is used to produce a final pH of the impregnant solution between 2.5 and 8.5, preferably about 5.0. At lower pH levels the solubility of the poly'hydroxyphenolics is depressed while at higher pH values the polyhydroxyphenolics are unstable towards air oxidation. The small concentration of OH- ions produced by the sodium hydroxide has been found insufficient to cause oxidation of the metal ions and darkening of the paper.

A recording paper containing organic compounds alone may be subject to discoloration in storage due to oxidation of the organic compound by oxygen in theair. Accordingly, the shelf-life of the paper containing the organic compound may be extended by the addition of stabilizers such as hydrazine or salts thereof, hydroxylamine or salts thereof, or thiourea, to the various formulations. These stabilizers act as oxidation inhibitors for the organic compounds.

Typical data is plotted in the curve showing the relationship between optical density and current for formulations in accordance with the teachings herein. Curve 1 shows the density of the mark when manganous chloride is used in the formulation of Example I but omitting the gallic acid. Curve 2 shows the density of the mark when gallic acid is used in the formulation of Example 1 but omitting the manganous chloride. Curve 3 shows the density of the mark in the formulation of Example 1. Curve 4, in dashed line, indicates the sum of the ordinates of curves 1 and 2. 7 As stated before, the mark formed when gallic acid and manganous chloride are used together shown by curve 3 is more intense than the sum of the results when either is used alone as shown by curve 4.

It is to be understood that, while the term paper has been used in this specification, the marking compounds are equally applicable to fabrics or any material of the same general nature which may be suitable for use in electrolytic recording processes. Accordingly, the

term electrolytic recording medium is to be construed 1. An electrolytic recording medium comprising an impregnated sheet containing as a marking composition a metal compound including a metal selected from the group consisting of Mu Co Ni Cr Ag Sn Pb T1 V said metal being capable of being oxidized to a higher oxidation state in the presence of base, and an organic compound selected. from the class consisting of polyhydroxyphenolics and aromatic polyamines which are capable of reacting in an electrically conducting solution with said metal in its higher oxidation state to form colored products. 7

2. An electrolytic recording medium according to claim 1 in which the organic compound is selected from the group of polyhydroxyphenolics and aromatic polyamines' V consisting of gallic acid, catechol, gentisic acid, hydro-' quinone, pyrogallol, o-phenylenediamine, p phenylenedi- I amine, benzidine and salts thereof, and tolidine hydrochloride.

3. An electrolytic recording medium according to claim 1 in which the pH of the composition is at least 2.5.

4. An electrolytic recording medium according to claim 1 in which the metal compound is selected from the group consisting of manganous salts, nickelous salts, and cobaltous salts.

5. An electrolytic recording medium according to claim 1 in which the organic compound is a polyhydroxyphenolic compound.

6. An electrolytic recording medium according to claim 1 in which a stabilizer is included.

7. An electrolytic recording medium according to claim 1 in which a stabilizer is included and which is selected from the group consisting of thiourea, alkyl derivatives of thiourea, dithiobiuret, hydrazine, salts of hydrazine, hydroxylamine, salts of hydroxylamine.

8. An electrolytic recording medium according to claim 1 in which the metal salt is manganese chloride, the polyhydroxyphenolic compound is gallic acid, a stabilizer is 6 included for the gallic acid, the composition having a pH of at least 4.5.

9. An electrolytic recording medium according to claim 1 in which the composition consists essentially in approximate parts by relative Weight of manganous chloride 1, gallic acid 1, and sodium chloride 5.0.

References Cited in the file or this patent UNITED STATES PATENTS 168,466 Edison Oct. 5, 1875 1,343,978 Little June 22, 1920 2,082,735 Heinecke June 1, 1937 2,358,839 Wagner Sept. 26, 1944 2,430,254 Solomon Nov. 4, 1947 2,570,096 Calkin Oct. 2, 1951 2,663,656 Miller et a1. Dec. 22, 1953 2,776,252 Schwartz Jan. 1, 1957 2,949,409 Richards Aug. 16, 1960 OTHER REFERENCES Bureau of Standards Circular C426, Inks, pages 32 and 33, Oct. 16, 1940. 

1. AN ELECTROLYTIC RECORDING MEDIUM COMPRISING AN IMPREGNATED SHEET CONTAINING AS A MAKING COMPOSITION A METAL COMPOUND INCLUDING A METAL SELECTED FROM THE GROUP CONSISTING OF MNII, COII, NIII, CRIII, AGI, SNII, PBII, TII, YIII, SAID METAL BEING CAPABLE OF BEING OXIDIZED TO A HIGHER OXIDATION STATE IN THE PRESENCE OF BASE, AND AN ORGANIC COMPOUND SELECTED FROM THE CLASS CONSISTING OF POLYHYDROXYPHENOLICS AND AROMATIC POLYAMINES WHICH ARE CAPABLE OF REACTING IN AN ELECTRICALLY CONDUCTING SOLUTION WITH SAID METAL IN ITS HIGHER OXIDATION STATE TO FORM COLORED PRODUCTS. 